Crude protein is the protein content estimated from total nitrogen multiplied by a factor, usually 6.25 for feed and 5.7 for wheat and flour.
In trade practice
It is the headline number for oilseed meals and feed grains. Nitrogen is measured by Kjeldahl or Dumas combustion (ISO 16634). The result changes with the nitrogen factor and with the basis, as-is or dry matter, so a figure without both is incomplete.
In a specification
State the minimum, the nitrogen factor, the moisture basis and the method.